Only real problem you will run into keeping the 96 computer is the crank sensor located in the oil pump. The 94 back cars didn't have it so you will have to either swap oil pumps to get the sensor in the older engine or take the dash out and swap the engine wiring harness over to the 94 and use the 94 computer.
Dash is easy to remove and it makes swapping the engine harness wires way easier. The advantage to the 94 computer is no second o2 sensor and a lot less emissions trouble codes in the computer so it doesn't complain when something as simple as the gas cap isn't on tight. The 96 computer can use the
scangauge to clear codes and whatnot and give you realtime mileage where the 94 will need the
mpguino to give you mileage data(mpguino also works on the 95+). the 94 just needs a jumper wire or fuse to read the codes so nothing else is needed.
If you use the 96 computer your best bet would be take the intake off the engine before pulling it and just leave it in the car. You also need the 96 distributor and oil pump. Everything else is the same that I can remember so stuff like the water temperature sensor should just plug in.
Going to the 94 computer means pulling the dash and taking the engine wiring harness out and splitting it from the body wiring harness then plugging in the 94 engine harness into the body wiring harness. I am pretty sure they are the same connectors so it should work easy. If not look on my site for wiring diagrams to adapt the connectors.
Both computers are very well tuned stock so you won't gain mileage from either one. the 96 has a better long term fuel trim setup so it might get you a tiny gain in mileage if something isn't working perfectly.